The term “fluid-filled domain”, as used herein, refers to a generalized notion for any fluid-filled hollow in a continuous medium. In particular, fluid-filled hollows include cracks, layers, faults, fractures and ruptures. The term “monitoring”, as used herein, refers to a generalized notion for actions on detecting, observing, predicting, analyzing or determining basic characteristics.
The present invention is applicable for wide variety of media (in particular, subterranean formations, construction elements, bones) and fluids (in particular, water, oil).
Monitoring of fluid-filled cracks is of great importance in various fields of human activity, for example, in extractive industry, medicine, construction engineering. Fluid-filled cracks in a medium can be both desirable and undesirable. Desirable fluid-filled cracks comprise artificially-made cracks, for example, hydraulic fractures intended for improving efficiency of oil production or for ore-body preconditioning in mining industry. Undesirable fluid-filled cracks comprise, in particular, large-scale natural subterranean cracks in the vicinity of cities and industrial objects, cracks in building constructions and bones.
In oil industry, hydraulic fracturing is widely used for improving well productivity by forming or extending channels from a wellbore to a reservoir. Hydraulic fractures are formed by hydraulically injecting a fracturing fluid into the wellbore under pressure. As a result, in a subterranean formation one or more tensile cracks are formed and filled with fluid, which normally leads to enhancement of oil production from the reservoir.
A fracturing fluid comprises proppant, whose low-size particles are added to the fluid to maintain a fracture open after termination of the fluid injection and pressure release in order to create a high-capacity drainage layer in the formation. Particles of sand or ceramic material are usually used as the proppant particles. For efficiency of usage, the fracture should propagate within a producing formation and should not extend to adjacent strata, furthermore, the crack should have sufficient sizes. Therefore, determination of the fluid-filled crack characteristic sizes is an important stage in optimization of the production process.
Sometimes the proppant forms an impermeable pack in the vicinity of the fracture tip, as a result the fracture ceases to propagate (“tip screenout”). Detection of the moment of tip screenout is an issue for an operator, who is to detect the moment to stop further proppant pumping.
Monitoring of fluid-filled domains is also of great importance in the context of detection, tracking and determination of characteristic sizes of large-scale natural cracks in subterranean formations, which cracks can cause earth surface erosion, cracks in various building construction elements such as slabs or diverse piers, which cracks can cause destruction of such building construction elements, as well as in the context of exploration and determination of characteristics of fluid-filled subterranean layers.
Presently characteristic sizes of fluid-filled cracks are determined using various technologies and methods. The most widely used is the technique of indirect determination based on the analysis of the pressure variation characteristics in the process of development and production. This technique is disclosed in, for example, Reservoir Stimulation, Third Edition, M. J. Economides and K. G. Nolte (Ed.), Chichester, UK, Wiley, 2000. A more reliable technique is the technique of acoustic investigation of cracks, which is used in field environment and based on the event location using passive acoustic radiation. This technique is disclosed in, for example, D. Barree, M. K. Fisher, R. A. Woodroof, “A practical guide to hydraulic fracture diagnostic technologies”, SPE 77442, submitted in Annual Technical Conference and Exhibition, San-Antonio, Tex., USA, 28.09.2002-02.10.2002.
Another technique for evaluation of the fluid-filled crack characteristic sizes consists in construction of a map of a free surface tilt. This technique is disclosed in the above-mentioned D. Barree, M. K. Fisher, R. A. Woodroof, “A practical guide to hydraulic fracture diagnostic technologies”. It includes tracking the deformation field in a formation surrounding a crack using tilt-meters.
All the above techniques imply complex preprocessing of acquired data, which preprocessing is needed for further determination of the crack geometrical characteristics based on models. As a result, the data processing complexity does not enable to perform fast interpretation of measurements and strongly limits the capabilities for real-time determination of the crack geometrical characteristics.
From U.S. Pat. No. 5,206,836 known is a method for determination of characteristic sizes of a subterranean crack intersecting an existing well based on exciting oscillations in a fluid filling the crack on a resonance frequency, wherein parameters used in calculations depend on dynamical characteristics of the fluid and a subterranean formation, as well as on geometrical characteristics. The fluid-filled subterranean crack geometrical characteristics are determined by inverting the crack physical properties obtained by modeling with the use of the data of observations of fluid pressure in the well.
The result provided by said method is achieved by interpreting the registered oscillations of the fluid pressure in the crack based on waves propagating in the fluid within the crack. A more detailed description of advantages of the method according to the invention in comparison with the method of U.S. Pat. No. 5,206,836 is given below after a detailed disclosure of the method according to the invention.
Thus, at present time there is a need in the art in fast and robust methods for monitoring of fluid-filled domains, enabling to implement real-time monitoring.